Transmission system



July 16, 1940.

' J; J. GILBERT TRANSMISSION SYSTEM Filed April 7, 1939 2 Sheets-Sheet 1MN 7 Q mw mm 4 mm A 3? E & Ew E m m ww 3 mm AMW m A m mm Aww mm A Q W ivw k wk 2k AK N vw wk vw AWN Q Q Q .s w\ km: nut flaw Q Q Q JNUMNM n A vH EW H UV H iv U W m vm ww v mm H mm ow 59 fiww n A H A n- A H AMHHQMA Ak m kw RE I m Q my Q vv w\ GE July 16, 1940. J. J. GILBERT TRANSMISSIONSYSTEM Filed, April 7, 1939 2 Sheets-Sheet 2 L l m .1 Wm. E W a l 0 m MNI. kw w 3 mm 2 QDQEU \\Q QYUN H h k H Q; P 330. vflw QM k\ mm kw m 3 H mm m t I 1 m m m Q A lull. B I vw vw m at INVENTOR J. J. GIL BERT A RNE YPatented July 16, 1940 John J. Gilbert, Douglaston,

Bell Telephone Laboratories,

N. 'Y.,- assignor to Incorporated,

New York, N. Y., a corporation of New York Application April 1,1939,Serial No. 266,528

7 clai s. (01. ne -175.31)

This invention relates to transmission systems, and, more particularly,to a transmission system including one or more unattended repeaterstations between attended stations or between the terminals of thesystem, and means and a method for testing for faulty repeaters atunattended stations.

Transmission systems are known in'whichaplurality of repeater stationsare located at geographically separated points along a transmission linebetween attended repeater stations or between the terminals of the line.If a repeater or amplifier at such an unattended station should fail, itwould be desirable to be able quickly to determine which one of them itwas, or to be able to determine prior to such a failure which of therepeaters at a plurality of unattended stations was faulty, for example,inits amplifying tube, before transmission became affected.

An object of this invention is so to arrange a transmission systemincluding a plurality of spaced attended and unattended repeaterstations, that the presence of a faulty repeater at an unattendedstation may be quickly and simply In accordance with the invention, atransmission system comprising a pair of transmission paths or lines fortransmitting electric wave energy in opposite directions and having aplurality of attended and unattended repeater stations at spacedintervals along the transmission line, is provided withmeansinterconnecting the transmission lines or paths of opposite direction ateach unattended station so that a preassigned different test signal foreach unattended station may be sent from and received at a test orattended station 'over the system and through each unattended repeaterstation to give information as to the operating condition of therepeater station. The interconnecting means may comprise a filter ateach unattended station connecting one line on the output side of there-' peater or amplifier therein to the other line on the input side ofthe repeater or amplifier therein.

A more complete understanding of the invention will be obtained from thedetailed description which follows read with reference to the appendeddrawings, wherein:

Fig. 1 shows a transmission system embodying the invention;

Fig. 2 shows the repeaters or amplifiers at an attended or at anunattended station; and

Fig. 3 illustrates how power may be supplied 55 from an attendedrepeater station in the sysdetermined from an attended or a teststation.

tem of Fig.1 to one or more unattended repeater stations.

Fig. 1 shows a transmission system extending between geographicallyseparated points or regions comprising a transmission path or line IIIfor transmitting electric wave energy in one direction, for example,from west to east, and another transmission path or' line fortransmitting electric wave energy in the opposite direction, i. e., fromeast towest. Such electric wave energy might be communications or othersignal energy superimposed on a wave of carrier frequency, and thetransmission paths could be adapted for the transmission of a singlecarrier wave in each direction, or for the transmission of a pluralityof carrier wave frequencies distributed over a preassigned frequencyband, for

- example, the system could be one adapted for twelve-channel carrieroperation utilizing a 12 kilocycles to kilocycles frequency band. Thetransmission lines may comprise pairs of insulated wires buried in theground; or, two pairs of conductors in a buried or a suspendedleadcovered cable; or, pairs'of wires especially 'insulated for polelineconstruction; or a pair of submarine cables.

A plurality of attended repeater stations l2, it are provided atgeographically separated points along the transmission lines, and aplurality of unattended repeater stationsl l, IE, it at smallerseparations are provided intermediate the attended stations. If thetransmission system is not a long one, the attended stations could bethe terminal stations of the system and only one unattended stationmight be required between them. At each repeater station there is anamplifier H for amplifying electric wave; energy incoming thereto andbeing transmitted in one direction, for example, from west to east, andan amplifier 18 for amplifying electric wave energy incoming thereto andbeing transmitted in the opposite direction, i e., from east to west.

At each unattended repeater station, the transmission paths of oppositedirection are interconnected by a filter or other signal discriminatingnetwork I9, 20, 2|, connecting the line in on the output side of anamplifier I! withthe line H on the input side of the amplifier l8. Eachnetwork I9, 20, 2| passes a different, preassigned,

- single frequency or a narrow band of frequencies outside of the usefulband of the amplifiers, i. e., in a system for transmission in the bandof 12 kilocycles to 60 kilocycles, outside of thatfrequency band andpreferably above 60 kilocycles. Suflicient transmission loss is providedin the overloading of the repeaters. These various single frequencies ornarrow frequency bands are furnished by a suitable sourc'e 22, forexample an oscillator, connected across the line ill at an attendedstation, and adapted to provide, under control of the attendant at theattended station, each of the unattended stations between it and thenext attended station with its appropriate preassigned frequency ornarrow frequency band, Recording, indicating or measuring means 23 isconnected across the line H at each attended station, whereby, asexplained more fully hereinafter, the frequency or frequency bandsoriginating in the source 22, transmitted to each unattended repeaterstation, passed by the lines-interconnecting network thereat, andreturned along line ii, afford evidence of the condition of theamplifiers at the unattended stations. In Fig. 1, attended station 32would be a test station in this respect for the unattended stations i6,i5, i6, and attended station iii, a test station in this respect forunattended stations (not shown) at points farther to the east along thetransmission paths.

Fig. 2 shows the circuit arrangement for an unattended repeater station.So far as concerns the amplifiers I l and 18, however, the attendedstations are the same. The amplifiers If, it are substantiallyidentical, and specific description of one is equally applicable to theother, like ele-' merits bearing corresponding identifying numerals. Theinput and output terminals of ampliher H are coupled to the line lthrough repeating coils 2d, and the corresponding terminals of amplifierit are coupled to line i I through repeating coils 25. The amplifier Ifis a single stage feedback amplifier incorporating stabilized negativefeedback as disclosed in H. S. Black Patent 2,102,671, issued December21, 1937,

the amplifying or -path of the amplifier being connected to the feedbackpath 23 through hybrid coils 21, 28, including the networks H, as taughtin the aforesaid Black patent and in the pending H. S. Blackapplication, Serial No. 114,390, filed December 5, 1936. The feedbackpath may include gain control means 29 and an equalizer network 30. Theamplifying device or tube 3! may be a pentode having a cathodeof theindirectly heated type. A network 32 may be connected in the cathodelead in accordance with D. D. Robertson Patent-.1,994,486, issued March19, 1935, to minimize any tendency for the amplifier to sing at somefrequency outside of the transmission range. Heating current for theheater elements of the amplifying devices and anode and screen gridpotentials are obtained over the transmission lines, either from theterminals of the system or from an attended station, through theconnections II and 34 coupling the mid-points of the line windings ofthe repeating coils 24, 25' in the lines III, II, respectively. The

impedances in the connections", 34 are of high and cathode heater orfilament heating current may be supplied to the unattended repeaters'tations from an attended station. The power supply may comprise thebatteries 38, the former having its positive terminal connected to themid-point of the linewinding of the repeating coil 24 at station 12, andits negative terminal together with the positive terminal of'battery 36connected to ground, the battery 36 having its negative terminalconnected. to the mid-point mediate rematers or for periodic testing ofthe condition of repeaters, by operations conducted entirely at anattended station. In the disclosed embodiment of the invention, station#2 constitutes the test station with respect to the unattended stations56,15, ifi. In case of an interruption which affects transmissionwithout a1- fecting, the power supply, the repeater station at fault maybe readily determined by using source 22 to apply to the line l0 testtone of appropriate frequency or frequencies corresponding to thepass-band of network l9, and detecting through the measuring device 23the extent to which the test tone is returned over transmission line Hto the test station. If the tone is received properly and satisfiespreassigned requirements indicative of satisfactory transmission andamplification condition of the amplifiers at the unattended station,another test tone corresponding to the pass-band of network 2G isapplied to the line It and picked off line I I; and likewise for thesucceeding unattended repeater station, the deviation in the detectedtest tone from its proper character if the particular unattendedrepeater station's amplifiers were not faulty, indicating whichunattended station is respon-- sible for the interruption intransmission over the system. The test tones should be chosen, ofcourse, in a frequency region where the net loss of the system is not sohigh as to prevent reception of the test tone through noise.

It is desirable not only to be able to determine at which unattendedstation trouble exists that impairs or interrupts transmission, but itis of importance to ascertain the condition of the amplifying devices ortubes so as to have forewarning of the necessity of replacing thembefore transmission is affected. The amplifier being of the stabilizednegative feedback type would be equalized over a much broader hand thanthe transmission hand. If the transmission band is 12 kilocycles-60kilocycles, the equalization provided might cover the range of 8kilocyclese-wdkilocycles. Periodic tests using 66 test tones in thefrequency region at the upper limit of the range for which the amplifieris equalized provide an index to the condition of the tubes before theeffect of impairment becomes appreciable in the transmission band. Thisfollows because there will be very little feedback at the highestfrequencies transmitted, and thus the gains of the amplifiers will varyaccording to the condition of the tubes.

Althoughi' this invention has been disclosed with reference to aspecific embodiment thereof, it will be understood that it is to beconsidered as limited only by the scope of the appended claims. I a

What is claimed is:

1. A transmission system comprising a test station; a transmission lineoutgoing from said test station; a transmission line incoming to saidtest station; a plurality of unattended repeater stations at spacedintervalsalong each of said 7 lines between geographically separatepoints; a repeater for outgoing transmission and a repeater for incomingtransmission being located test station; a transmission line incoming tosaid test station; a plurality of unattended repeater stationsat spacedintervals along each of said lines; a repeater for outgoing and arepeater for incoming transmission being located-at each unattendedstation; filter means connected between the outgoing and the incomingtransmission lines at each unattended station on the output side of theoutgoing repeater and the input side of the incoming repeater, each ofsaid filter means having a diiferent pass-band outside of thetransmission band; and means at said attended station for sending a testfrequency band over said outgoing line, through the filter adapted topass said band and said incoming line to measuring equipment at saidattended station for determining the condition of the repeaters at eachunattended station.

3. A transmission system comprising a test station; one or moreunattended repeater stations at spaced intervals between said teststation and a remote point; a transmission line, for conducting signalwaves from station-to-station in one direction through said system, atransmission line for conducting signal .waves from station-to-stationin the reverse direction through said system; a repeater at each of saidunattended stations for repeating the signal waves in one direction, anda repeater for repeating the signal waves in the reversedirection; andmeans interconnecting the transmission lines at each unattended repeaterstation for frequencies outside of the band of the signal waves thesystem is designed to transmit.

4.11'1 a transmission system, a transmission line for transmittingsignal waves of a presssigned frequency band in one direction; atransmission line for transmitting said frequency band in the oppositedirection; a repeater in each transmission line, said repeaters beinglo-v cated at the same station; and means at said repeater stationinterconnecting said transmission lines for a signal wave of frequencycontent outside of said preassigned frequency band, whereby said latterwave transmitted from one end of the system to said repeater station isutilized to test the condition of the repeaters thereat.

'5. In a transmission system comprising a test station; and one or moreunattended repeater stations between the test station and ageographically remote point; a transmission line for conducting signalwaves from station-to-station in one direction through said system; atransmission line for conducting signal waves from station-to-station inthe opposite direction through said system; a repeater at each of saidunattended stations for repeating the signal waves in one direction, andanother repeater for repeating signal waves in the opposite direction;and means operatively interconnecting the transmission lines at eachunattended repeater station for frequencies outside of the band of thesignal 1 waves the system is intended to transmit; the method of testingthe condition of the repeaters at each unattended station whichcomprises transmitting over one transmission line to each repeaterstation a different preassigned signal Wave outside of the transmissionband and measuring the character of the signal received at said teststation over the other transmission line for each of said unattendedrepeater stations.

6. In a transmission system comprising a transmission path for signalwaves to pass in opposite directions, and a repeater stationintermediate the ends of said path, said station including repeatermeans for signal waves passing in each direction; the method of testingthe condition of said repeater means which comprises impressing at oneend of the path a test signal wave of a frequency outside the band offrequencies that the system is designed to transmit, causing said testsignal wave to pass through and around said repeater means to return toits originating point, and measuring the strength of the signal wavereceived at its originating point.

'7. In a transmission system having one or more unattended repeaterstations and an attended repeater or test station, means interconnectingthe transmission paths of opposite direction at each unattended stationso that a preassigned different test signal for each repeater stationmay be sent from and received

